User terminals for use in mobile communications, e.g. portable radios or telephones or radios carried in vehicles, conventionally support operation in a single RF (radio frequency) band, i.e. the operational band of the system. Such terminals employ an antenna to transform RF signals in an operational frequency band between a bound (conductor guided) form and a radiated form for over-the-air transmission. The antenna comprises a resonator designed to provide electrical resonance in the operational frequency band. Typically, a conventional resonator has a monopole or quarter wavelength linear conductor form.
Different mobile communication systems typically operate in different RF bands. Often the RF bands are in significantly different parts of the frequency spectrum. Some advanced terminals are being designed to provide operation in different systems and/or frequency bands and to provide continuous mobile connectivity whilst switching from one system/frequency band to another. Thus, antenna arrangements are required for use in such terminals which can operate in different frequency bands in one or more communication systems. Such arrangements are required to have a shape and size which is suitably compact and lightweight for user satisfaction.
Antenna arrangements employing resonators of conventional form have been found to be unsuitable for use in supporting communications in multiple systems/frequency bands owing to lack of satisfactory bandwidth. Resonators of unconventional form are known which provide multiple resonances but such resonators do not show sufficient bandwidth and operational efficiency when operated in widely different frequency bands. Furthermore, such resonators generally have a shape and size which does not easily fit into the terminal in a sufficiently compact manner.